Protozoan Pathogens

Question 1

Entamoeba histolytica tissues invaded

Answer 1

Small intestine, can invade deeper tissues (liver, less commonly brain, lungs)

Question 2

Proportion of infected in developing world

Answer 2

5-10% of population

Question 3

Can entamoeba histolytica be asymptomatic?

Answer 3

Yes - many infections are asymptomatic

Question 4

Entamoeba histolytica spread

Answer 4

Faecal-oral person-person spread

Question 5

Entamoeba histolytica receptor

Answer 5

Digalactose residue on intestinal cells. Attaches with a surface lectin.

Question 6

Entamoeba histolytica mechanisms for evading immune system:
1)
2)

Answer 6

1) Contact-dependent pore-forming toxin inserted into cells

2) Secretes factors which breaks down IgA, IgG

Question 7

Immune mechanisms against entamoeba histolytica:
1)
2)

Answer 7

1) Mucus covers digalactose residues on intestinal cells

2) Cell-mediated immunity

Question 8

Entamoeba histolytica pathogenesis:
1)
2)
3)

Answer 8

1) Binds to cells with surface lectin-digalactose residues
2) Contact-dependent pore-forming toxin inserted
3) Amoeba ingests lysed cell

Question 9

Entamoeba histolytica treatment

Answer 9

Metronidazole

Question 10

Entamoeba histolytica lab diagnosis:
1)
2)
3)

Answer 10

1) Look for cysts in stool sample (microscopy)
2) Stool immunoassay for parasite antigen
3) Serology of patient sera
- Can’t distinguish between recent infections

Question 11

Entamoeba histolytica symptoms

Answer 11

Dysentary

Question 12

Giardia lamblia symptoms

Answer 12

Watery diarrhoea, greasy, foul-smelling stools

Question 13

Giardia lamblia transmission

Answer 13

Zoonosis. Transmitted from animals or infected humans

Question 14

Diseases caused by giardia lamblia

Answer 14

Traveller’s diarrhoea

Question 15

Difficulties in killing giardia lamblia

Answer 15

Acid-, chlorine-resistant

Question 16

Giardia lamblia pathogenesis:
1)
2)
3)
4)

Answer 16

1) Cysts ingested
2) Excystation in small intestine, attach to intestinal wall with ventral sucking disc
3) Intestinal absorptive capacity decreased as increased numbers of trophozoites attach
4) Host responses include lymphocyte invasion of mucosal cells, shortening of microvilli

Question 17

Giardia lamblia lab diagnosis:
1)
2)

Answer 17

1) Microscopy of stool samples

2) Antigen detection assay

Question 18

Giardia lamblia treatment

Answer 18

Metronidazole

Question 19

Cryptosporidium symptoms

Answer 19

Watery diarrhoea

Question 20

Cryptosporidium life-cycle:
1)
2)
3)
4)
5)

Answer 20

1) Oocysts ingested (sporulated oocyst contains 4 sporozoites)
2) Excystation in GIT, parasitisation of epithelial cells
3) Asexual replication
4) Sexual replication
5) Thick-walled oocysts excreted, thin-walled oocysts autoinfection

Question 21

Cryptosporidium sexual reproduction

Answer 21

Macrogamonts (F) fertilised by microgamonts (M)

Question 22

Cryptosporidium virulence factors

Answer 22

Little known.
Surface glycoproteins and lectins involved
Doesn’t invade deeper than microvilli
Produces proteases

Question 23

Cryptosporidium lab diagnosis

Answer 23

Microscopy for acid-fast cysts

Stool antigen detection assay

Question 24

Cryptosporidium treatment

Answer 24

Nitazoxanide (similar to metronidazole)